1. Field of the Invention
This invention pertains to passenger elevators generally, and more specifically to an electrical control circuit for powering an elevator hoist motor.
2. Description of the Related Art
In cities around the world, real estate has become more valuable with increases in population density. To best utilize precious land area, architects and engineers have designed and erected buildings of ever increasing heights. These tall buildings are not new, some having existed for more than a century. In order to provide reasonable access to the upper floors of these buildings, elevators have been provided as a matter of course. Hoist motors provide the actual raising and lowering forces applied to the elevator car, while motor-generators convert A/C power from an electrical supply line to DC and are used as part of the control of both speed and direction of the hoist motor. As one will recognize immediately, electronic circuits capable of controlling the large hoist motors used with elevators were not available to building designers until recently. Instead, large switch banks and massive motor-generator sets provided the necessary interface to a hoist motor.
Many of the tall buildings were and continue to be constructed with long-life materials such as reinforced concrete and steel. As a result, these buildings have outlasted the useful life of the motor-generator sets. With the advent of more advanced and lower cost electronic devices, repair or replacement of motor-generator sets with identical motor-generators is no longer preferred. A modern Solid State Drive (abbreviated SSD) performs the basic functions of the older motor-generators while offering added advantages. For example, the SSD may be used to very precisely control parameters such as accelaration and deceleration of the elevator car. Compensation for variable hoist motor parameters such as winding impedance and field strength may occur instantaneously, or, in some designs, may not be required at all.
Unfortunately, replacement of the motor-generator set has, in the prior art, also necessitated replacement of the entire elevator control system. Replacement of the existing controls which are used in part to drive motor-generator sets is very costly and unduly burdensome to building owners.